Patent Literature 1 discloses a method for non-invasively measuring the interior of a scattering-absorption body. In this measurement method, light incidence means causes pulsed light to irradiate, at a light incidence position, a scattering-absorption body that comprises a region to be measured and a region not to be measured. The pulsed light, while being scattered, reaches then a light detecting position, through respective optical paths, and is detected by light detecting means. At least one from among the light incident position and the light detecting position is a plurality of positions. The variation amount of the absorption coefficient of the region to be measured alone is calculated by using a temporal profile of the detected light and assuming that the partial optical path length of propagation through the region not to be measured is constant, irrespective of the optical path.
Non Patent Literature 1 indicates that in measurements by near-infrared spectroscopy (NIRS) the mean optical path length of light that propagates through the body varies depending on tissular structure, i.e. muscle or fat, the amount of blood and muscle morphology.
Non Patent Literature 2 discloses the feature of measuring beforehand fat thickness by a separate method, and correcting then, according to that fat thickness, measurement results of hemoglobin amount by near-infrared spectroscopy.